This invention relates to a black matrix color picture tube and a method for its fabrication and particularly to a high-contrast black matrix color picture tube and a method for its fabrication.
The phosphor screen of a so-called black matrix color picture tube has on its faceplate the formation of a nonluminous, light-absorptive powder layer (black matrix) for partly covering the phosphor layer so that the phosphor layer appears through aperture sections (matrix holes).
Among the two major methods of forming such a phosphor screen, one is the wet process, which is typically as follows. On the inner surface of the faceplate, a photoresist is applied to form a film, and portions of the photoresist film where phosphor will be laid are hardened. After the development process, carbon suspension is applied to it to form a carbon application film and, thereafter, a removal agent is poured onto it to remove the hardened photoresist together with the overlaying carbon layer so that matrix holes are formed. Next, the photoresist slurry including phosphor is applied to form a film and the application film at positions where the phosphor will be laid is hardened. Following the development process, a phosphor layer is formed in the matrix holes. For making a phosphor layer of three colors, i.e., red, green and blue, the above process is repeated for each type of phosphor. Finally, the baking process is conducted to eliminate organic substances.
The second is the dry process which was developed by some of the inventors of the present invention (see JP-B-57-20651 which corresponds to JP-A-53-126861). This method typically includes the processes of forming an application film including aromatic diazonium salt, which exhibits adhesion or tackiness by being exposed to light, on the faceplate, and exposing it to the light radiation so that phosphor is deposited in the irradiated portions. For making a phosphor layer of three colors, the light irradiation and following processes are repeated three times. Next, the entire application film is exposed to light and carbon is deposited in portions other than the phosphor layer so that a black matrix is formed. Finally, a fixing process using a polymer aqueous solution, etc. is conducted so that these layers are made insoluble in water. In case of a striped phosphor pattern, it is also possible to form a black matrix layer before forming the phosphor layer.
In the formation of a phosphor screen by any of the above methods, there is created a gap partly between the phosphor layer and black matrix layer and the faceplate. When the light is incident from the outside (from the viewer's side), part of the light is reflected on the outer surface of the faceplate, and, because of the presence of the gap, part of the light is further reflected on the inner surface. The inner surface reflection, which depends on the refractivity of the faceplate, is over as much as 3-5% of the incident light. Therefore, suppression of the inner surface reflection is desired.
A method of reducing the inner surface reflection has been proposed, in which a material having virtually the same refractivity as the faceplate material, e.g., water glass, is filled in the gap between the faceplate and the black matrix layer. See, for example, JP-A-57-115749. This conventional technique, however, has a problem in that the water glass filled in the black matrix layer penetrates into the phosphor layer, causing a decrease in the light intensity of the phosphor.
Sticking of water glass to the phosphor surface by capillary action is unavoidable, and conceivably electron rays emitted by phosphor are retarded by the water glass, resulting in a decreasing intensity of the phosphor. Water glass does not much exist in the portion of the phosphor layer, but instead bubbles rest there and the inner surface reflection cannot be prevented completely in this portion. It is also undesirable to use water glass because of the mismatch of refractivity between water glass and the glass of the faceplate.